1. Technical Field
The present invention relates to a light emitting device in which a plurality of light emitting elements is mounted on a substrate. More particularly, the present invention relates to a light emitting device in which a plurality of light emitting elements mounted on a substrate is electrically connected to each other by thin metal wires.
2. Related Art
Conventionally, a light source such as an incandescent light bulb, a fluorescent lamp, and a high-pressure discharge lamp has been used as lighting equipment. However, recently, from the viewpoint of low power consumption and long lifetime, an illumination light source using an LED (Light Emitting Diode) element has been popular. An LED light source configured by one LED element has low emission intensity. Accordingly, a plurality of LED elements is used in order to obtain the emission intensity comparable to the conventional light source. In order to realize an LED illumination light source with high output, a mounting density of the LED elements onto a substrate tends to increase.
In such an LED illumination light source, various methods for arranging LED elements have been proposed (e.g., see Patent Documents 1 to 4). Among these methods, in order to achieve uniformity of the emitted light from the LED illumination light source, in many cases, an LED element mounting region is formed in a circular shape and the LED elements are regularly arranged. FIG. 1 illustrates an LED illumination light source in which LED elements are regularly arranged. In an LED illumination light source 10 shown in FIG. 1, a substrate 1 includes a bonding pad 1a for electrical connection with multiple LED elements 2, an external connection pad 1c for electrical connection with the outside of the LED illumination light source, and a wire 1b for connecting the bonding pad 1a and the external connection pad 1c. An annular dam portion 3 is formed on a surface of the substrate 1 and a plurality of LED elements 2 is regularly arranged in a matrix shape of twelve rows and seven columns at a region inside the annular dam portion 3. In this example, seventy two LED elements 2 are arranged. When an external voltage is applied to the external connection pad 1c, current flows through each LED element 2 so that each LED element emits light.
Recently, from the demand for a high-output LED illumination light source, an amount of heat generated from each LED element tends to increase. For the LED element, it is generally known that the emission intensity is lowered and thus reliability is degraded when the junction temperature becomes higher.
Patent Document 1: JP-A-2003-124528
Patent Document 2: JP-A-2013-004739
Patent Document 3: JP-A-2013-118292
Patent Document 4: JP-A-2013-201355